# What is the difference between O2 and O3?

Oxygen gas ${O}_{2}$ is very stable Ozone ${O}_{3}$ is very unstable.
Ozone is necessary for living things in that it protects living things from harmful solar radiation. Ozone being unstable reacts with and absorbs solar radiation breaking back down into normal ${O}_{2}$ Oxygen. Without an Ozone layer solar radiation would cause substantial DNA damage to living organisms. It is possible that without Ozone life on the surface of the earth would not be viable.